<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<input type="text" placeholder="半径" id="a"/>
		<input type="text" placeholder="周长" id="b"/>
		<input type="text" placeholder="面积" id="c"/>
	</body>
	<script>
		var q= prompt('请输入圆的半径');
		var p = Math.PI;
		document.querySelector('#a').value = q;
		document.querySelector('#b').value = (q * 2 * p);
		document.querySelector('#c').value = (p * q)*(p * q);
	
	</script>
</html>
